The world's second-ranked player did not have it easy, however, needing a tiebreaker in the second set to pull off a victory.
Meanwhile, his next opponent, Juan Martin del Potro, got back to his winning ways, eviscerating Janko Tipsarevic. With that win, del Potro keeps himself in a position to advance to the semis, but he certainly won't have it easy against Federer, who has looked fantastic thus far.
In doubles action, the duo of Leander Paes and Radek Stepanek defeated Marcel Granollers and Marc Lopez, while Bob and Mike Bryan got back to their winning ways against Aisam-Ul-Haq Qureshi and Jean-Julien Rojer.
Though each of the day's matches had their moments, it was mostly a day of expected results in London. With that in mind, here's a look at a complete recap of all of Day 4's action.
SINGLES - Group B
(2) Roger Federer def. (4) David Ferrer; 6-4, 7-6 (5)
(6) Juan Martin del Potro def. (8) Janko Tipsarevic; 6-0, 6-4
DOUBLES - Group A
(3) Leander Paes and Radek Stepanek def. (6) Marcel Granollers and Marc Lopez; 7-5, 6-4
(1) Bob Bryan and Mike Bryan def. (7) Aisam-Ul-Haq Qureshi and Jean-Julien Rojer; 7-5, 6-4
Federer Continues Dominance vs. Ferrer
Despite facing his toughest match of the World Tour Finals to date, Federer was able to continue his hot streak and lock himself up a place in the semifinals.
The two-time defending champion of the event is now 14-0 in his career against his counterpart, but it seems like every match these two play gets closer. Both dominating each other with a strong service game, neither Federer nor Ferrer was able to get a break point in a hotly contested second set.
For the tournament, Federer remains the only singles competitor who is yet to lose a set. With a matchup likely coming against Andy Murray in the semifinals, the Swiss star will have to keep his composure and avoid an upset against del Potro when he finishes Group B play.
Meanwhile, things still look good for Ferrer's advancement. He's already beaten del Potro and will get a match against Tipsarevic next, who seems to be slightly overwhelmed at this level of competition.
Del Potro Dominates, Keeps Hopes Alive
In what can only be deemed one of the more dominating performances we've seen in the tournament, del Potro dispatched of Tipsarevic quite easily on Thursday.
The 24-year-old Argentinian was brilliant from the opening serve, looking like the same player who has shown so much promise at times. Behind a strong service game and great defensive play, del Potro left Tipsarevic flailing in a first-set victory that flew by.
That dominance was essentially a precursor to the second set, which seemed to be two men going through the motions toward an inevitable result. Now essentially eliminated from the tournament, Tipsarevic will be playing for both pride and hope that the breaks fall his way.
Meanwhile, del Potro has a chance to shock the tennis world with a victory over Federer. If that happens, it will make for a mighty interesting story for a kid who has all the talent in the world, but is yet to completely put it together.
Day 5 Schedule
(2) Max Mirnyi and Daniel Nestor vs. (5) Mahesh Bhupathi and Rohan Bopanna (6:00 a.m. ET)
(4) Robert Lindstedt and Horia Tecau vs. (8) Jonathan Marray and Frederik Nielsen (12:00 p.m. ET)
(1) Novak Djokovic vs. Tomas Berdych (not before 7:45 a.m. ET)
(3) Andy Murray vs. Jo-Wilfried Tsonga (not before 1:45 p.m. ET)